1. Field of the Invention
The present invention relates to a film forming apparatus that forms a porous insulation film and a non-porous insulation film on a substrate such as a semiconductor wafer.
2. Description of the Related Art
An insulation film is formed on a substrate in such a manner that an insulation film material is coated on the substrate, dried, and heated. A system that integrally performs a series of processing steps such as a coating process, a drying process, and a heating process for an insulation film material is known.
Recently, the improvement of the insulating characteristic of an insulation film has been required. In order to meet the requirement, a porous insulation film has been used. For such a coating material, a material such that contains porogen in an insulation film material like methyl silsesquioxane (hereinafter abbreviated as MSQ) is used. In addition, after the coating process for such a material is performed, a heating process is performed under a different condition (for example, at different temperature) from the conventional heating process for a non-porous insulation film.
In the dual damascene method, which has been widely used in recent years, to improve the etching accuracy or to form a hard mask and the like, two or more types of insulation films are laminated. Thus, usually, both of the non-porous insulation film and the porous insulation film are formed on one semiconductor wafer. Since the condition for forming the porous insulation film is different from the condition for forming the non-porous insulation film, a separate system from a system for forming the non-porous insulation film has been provided for forming the porous insulation film. Thus, the facility becomes large. In addition, a wafer has to be transferred between the systems and, as a result, the process is not effectively performed taking a long time to complete.
In general, after the porous insulation film is formed, in a case of laminating another insulation film such as the non-porous insulation film thereon, the insulation film is formed with CVD (Chemical Vapor Deposition) method. By the CVD method, a very thin film is formed in comparison with a film formed with a method of rotating the substrate, namely spin coating method. Since the front surface of a porous insulation film as a lower layer is largely rugged, an insulation film as an upper layer laminated by the CVD method is also largely rugged. As a result, a flat film cannot be formed.